My understanding is that nfs doesn't have the concept of a user and password (unlike smb). Access is controlled on an ip basis by the host, so I suspect you need to make sure the humax's ip address is explicitly enabled or in the ip range on the server. I don't know how this is set up on your NAS, but if you have low level access it involved editing
/etc/exports, /etc/hosts.allow, and /etc/hosts.deny
Alternatively if your NAS can do smb filesharing rather than nfs that could be worth a go.
Hope that helps...